Study of Sewage Sludge Pyrolysis Mechanism and Mathematical Modeling

Abstract

The pyrolysis of sewage sludge, with and without ZnCl₂ activation, was monitored using TGA-FTIR, with the results utilized in a proposed decomposition mechanism. For the pyrolysis of sludge without ZnCl₂ activation, three global stages of mass loss occurred and are proposed as dehydration, initial depolymerization, and deep degradation. For the pyrolysis of sludge with ZnCl₂ activation, apart from these three stages, an additional mass loss stage could be also observed at high temperature. It is suggested this results from the evaporation of ZnCl₂. To make a comparison between these two cases, it was found that the pyrolysis of sludge with ZnCl₂ activation had a longer dehydration phase and a shorter degradation phase. Based on the speculated mechanism, a kinetic model of four consecutive competitive reactions was adopted to simulate the pyrolysis of sewage sludge with and without ZnCl₂ activation. Globally, the proposed model was able to fit the experimental data very well for both cases, with the correlation coefficients above 0.99.